Thermal and Structural Aspects of the Hydride-Conducting Oxyhydride La₂LiHO₃ Obtained via a Halide Flux Method

Abstract

Oxyhydrides, in which oxide and hydride anions share the same anionic lattice, are relatively rare compounds. La₂LiHO₃ belongs to this family. We report the synthesis of La₂LiHO₃ by means of an alkali halide flux method, which allows the production of larger quantities of material relative to the usually adopted synthesis routes. Powder X-ray and neutron diffraction studies show that La₂LiHO₃ adopts an n = 1 Ruddlesden-Popper (RP)-type structure with an orthorhombic distortion (Immm) due to hydride and oxide anion ordering. No sign of polymorphism is observed. La₂LiHO₃ is seen to decompose in an oxygen atmosphere at ∼450 °C into La₂LiO_3.5. We show that the high mobility of hydride anions close to the decomposition temperature is likely the main factor in inducing the oxidation. The crystal structure of La₂LiO_3.5 is also determined and takes an n = 1 RP-type structure with an orthorhombic distortion (Fmmm). This newly reported large-scale synthesis approach, combined with the proven high thermal stability, is a key factor for potential practical applications of this oxyhydride in real devices.